1. Field of the Invention.
The present invention relates to digital electronic circuits. More specifically, the present invention relates to circuits for performing logic functions in user-programmable integrated circuits, and to circuits for implementing a wide variety of user-selectable combinatorial and sequential logic functions.
2. The Prior Art
Programmable logic blocks which are capable of performing a selectable one of a plurality of user-selectable logic functions are known in the prior art. U.S. Pat. No. 4,910,417 to E1 Gamal et al., assigned to the same assignee as the present invention, and U.S. Pat. No. 4,453,096 to Le Can et al., disclose logic modules composed of multiplexers capable of performing a plurality of combinatorial functions.
While these circuits provide a degre of flexibility to the designer of user-programmable logic arrays, there is always a need for improvement of functionality of such circuits.